Watches on the ship seem to have slowed down since we began shooting 7 days ago. No more hustling about the deck helping the Scripps team build seismometers as the Langseth speeds towards the next drop site. Now we zig-zag along at a slow steam steadily setting off small underwater explosions that are fueled by compressed air. Notes are casually recorded every half-hour to keep track of our progress. Below deck in the main lab, the constant humming of the ship and the occasional murmurs of background conversations makes it easy to let your mind wander. Like clockwork, the airguns sound off with a loud thud that gently rattles the boat. Another 90 seconds has past. The remaining energy from the sound source is now rattling around miles beneath the seafloor and being recorded by the seismometers we dropped into the Aegean last week. I am told that each of the 36 airguns squeeze air to a pressure of 2000 psi and the total volume of compressed air is 6600 cubic inches. What does that mean? To pass the time I cast these values into more whimsical units. The ideal gas law predicts the volume of our airgun array at standard pressure (1 atmosphere) would be 15 cubic meters. In other words, enough air to fill approximately one-thousand balloons***. That would make for an interesting seismic source. BANG! Another minute and a half has passed. The noise is akin to several people simultaneously hammering the hull. I have spent enough time day dreaming for now. I am off to clean up some of the noise in the bathymetry data we are currently collecting.

Sleepily,

Brandon VanderBeek

Airguns at sunset (#sunsoutgunsout)

***The assumption is made that balloons have no resistance to inflation. In reality, the pressure within a standard rubber balloon is slightly greater than outside (by ~0.005 atm). Such a small pressure difference does not significantly alter the estimate made above.